This invention relates to a novel method for manufacturing a touch screen linearization pattern and particularly to a method of producing a linearization pattern that is capable of increasing a resistance ratio of a glass surface unit square against two ends of the linearization pattern.
Presently, voltage sensing type touch screens and current sensing type touch screens have been widely used in desk top computers, handheld computers or notebook computers. Users may write, draw pictures or select various functions or press command keys on the screen to generate electric signals and input into the computer to perform processes desired. When in use, the computer carries out switching of functional windows on the screen, and users do not have to operate the computer through the keyboard.
The touch screen set forth above (as shown in FIG. 1 for a traditional current sensing type touch screen) usually includes a glass layer 1, a conductive membrane layer 2, a linearization pattern 3, an isolation layer 4, a four wire silver printing layer 5 and a tail cable 6 connecting to a controller. The controller outputs four equal voltages to four linearization ends of the touch screen to measure current variation.
When different points of the touch screen are touched, the current at the four ends will have different changes. Through measuring the current variation, the controller can determine the touched position. Detailed operation principle may be found in U.S. Pat. No. 4,293,734.
In practice, the design of linearization pattern directly affects the accuracy, price and occupied space of the touch screen. Earlier linearization patterns consisted of discrete resistor elements linking to the border area of the touch screen to form a resistor network. This type of resistor network is not desirable either in manufacturing or final accuracy of the touch screen. Later, a technique of forming linearization patterns by printing was developed. Reference can be found in U.S. Pat. No. 3,798,370. However, same as before, the resulting linearization patterns occupy a relatively large border area of the touch screen and result in less useful area for the touch screen. In the present LCD development, border area becomes smaller constantly, and large size linearization pattern will have little or no market acceptance.
In the past, there was a concept for making the touch screen linearization pattern disclosed in U.S. Pat. No. 3,591,718. However it does not provide a practical method for manufacturing, and the concept never materializes commercially.
There is another type of touch screen (as shown in FIG. 2. a traditional voltage sensing type five wire touch screen) which includes a glass layer 7, an Indium Tin Oxide (ITO) conductive layer 8, a linearization pattern 9, a set of insulation points 10, an isolation layer 11, a four wire silver printing layer 12, another isolation layer 13, another ITO conductive layer 14, a plastic membrane layer 15 and a tail cable 16 linking to a controller. In operating principle, the lower ITO links to an even electric field of 0-5V in X-axis direction. When the touch screen is touched, the upper ITO layer contacts the lower ITO layer and measures the voltage value. The voltage ratio represents the positional ratio on the touch screen in that direction (X-axis). For instance, 3V represents the touch point located at 60% of the total length in the X-direction. When measuring of one direction (i.e. X-axis) is finished, the controller panel converts the lower ITO to an even electric field of 0-5V in Y-axis direction, then uses the lower ITO layer to measure the voltage value of touch point at the upper layer and measure the position in another direction (Y-axis). Reference details can be found in U.S. Pat. No. 3,798,370. This type of touch screen also needs linearization pattern to increase accuracy. In this type of touch screen, ELO""s five wire resistive touch screen is the most popular on the market. ELO""s linearization pattern is made by forming the resistor network from separated silver paste, and adding and removing some of the conductive sputtering layer to increase the accuracv of the linearization pattern used on the touch screen. However, ELO""s touch screen still has a lot of linearization deficiency at the border corners. The process of removing the conductive layer also increases the production cost of the touch screen.
It is therefore an object of this invention to overcome the foregoing disadvantages by blending high conductive material such as silver powder and carbon powder and contact agent solvent to form a printing ink, then using the ink to print an even resistor line at the border area of the touch screen to form a connected resistor network to serve as linearization pattern thereby to increase accuracy of the touch screen and reduce production cost and reduce the border area being used.
Another object of this invention is to use other high conductive high conductive metallic material such as copper powder. By changing relative material contents, a desirable resistance coefficient may be obtained thereby to produce a linearization pattern desired. During manufacture of the material composition arrangement, the size and thickness of the pattern may be used to compensate the conductivity overshoot or deficient of the material to ensure that the final resistance ratio of each square of glass surface against two ends of the linearization pattern reaches about ten.
In one aspect, this invention provides a blended material for printing the required resistance value to couple with existing ITO conductive glass now available on the market to produce a low cost touch screen that has high accuracy and more useable area.